[PATCH] getloadavg: use sysinfo() instead of /proc/loadavg

[PATCH] getloadavg: use sysinfo() instead of /proc/loadavg

[Alexander Monakov]

Based on a patch by Szabolcs Nagy.
---
This is a followup to a recent IRC conversation.  getloadavg() doesn't really
need to open a file in /proc, since a sysinfo() syscall should suffice.  Based
on a patch by nsz, slightly adjusted.  Return value of sysinfo() call is not
checked, since the only documented failure is with EFAULT.

 src/legacy/getloadavg.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/src/legacy/getloadavg.c b/src/legacy/getloadavg.c
index 43a8c9e..ff06de0 100644
--- a/src/legacy/getloadavg.c
+++ b/src/legacy/getloadavg.c
@@ -1,18 +1,14 @@
 #define _GNU_SOURCE
 #include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
+#include <sys/sysinfo.h>
 
 int getloadavg(double *a, int n)
 {
-	int i;
-	double b[3];
-	FILE *f = fopen("/proc/loadavg", "rbe");
-	if (!f) return -1;
-	i = fscanf(f, "%lf %lf %lf", b, b+1, b+2);
-	fclose(f);
-	if (n > i) n = i;
-	if (n < 0) return -1;
-	memcpy(a, b, n * sizeof *a);
+	struct sysinfo si;
+	if (n <= 0) return n ? -1 : 0;
+	sysinfo(&si);
+	if (n > 3) n = 3;
+	for (int i=0; i<n; i++)
+		a[i] = 1.0/(1<<SI_LOAD_SHIFT) * si.loads[i];
 	return n;
 }
-- 
2.1.3

Re: [PATCH] getloadavg: use sysinfo() instead of /proc/loadavg

[Rich Felker]

On Tue, Feb 24, 2015 at 09:44:07PM +0300, Alexander Monakov wrote:
> Based on a patch by Szabolcs Nagy.
> ---
> This is a followup to a recent IRC conversation.  getloadavg() doesn't really
> need to open a file in /proc, since a sysinfo() syscall should suffice.  Based
> on a patch by nsz, slightly adjusted.  Return value of sysinfo() call is not
> checked, since the only documented failure is with EFAULT.

Thanks. Committed.

Rich